In refuse incineration plants, various combustion grates are used. In larger plants, clamped or compressed grates are frequently used.
In the case of non-clamped or non-compressed grates, grate bars which have expansion play on their sides are customarily used, as known from Federal Republic of Germany Patent Document DE A1-26 52 475. This expansion play is generally distributed non-uniformly over the entire width of the grate. On the sides facing the furnace walls, there is generally a further air gap provided to allow expansion play. In the case of these known grates, the air gaps lead to an uncontrolled admission of air from the bottom or undergrate air region to the material being incinerated.
In addition to the problem of uncontrolled admission of combustion air or uncontrollable pressure of the furnace atmosphere, dropping of the material being incinerated through the slots is frequently observed, leading to a corresponding deposit of ash below the grate and the subjecting of the structural parts located below the grate to unintended elevated temperatures.
One particular problem is caused by the deposits of nonferrous metals which melt at a lower temperature and flow through such slots between and alongside the grate bars or, for instance, steel scrap which becomes jammed between the grate bars and thus restricts the mobility of the bars.
Therefore, grate bars which have been milled flat on the side and lie alongside of each other are known, which are connected by individual attachment devices, such as screws, in order to form a slot-free combustion grate surface, as shown in Federal Republic of Germany Patent Document DE A1-38 13 441.
Reciprocating grates for refuse incineration furnaces having, transverse to the grate, rows of grate bars which are movable in the direction of advance of the grate, are also known from Swiss Patent Document CH 585 372. The grate bars are clamped resiliently together without any gap, according to this method. This furnace has a shield which limits the grate on the side and which is also pressed by screw springs against the grate bars.
It is also known to use a system in which shields press the grate bars together by means of a clamping device which rests against the furnace wall. The clamping device is formed in this case of a plurality of hinges with telescopic guides under spring action which lie between them, the hinges being fastened to the shield and to the furnace wall. This system is very expensive to construct due to its large number of component parts.
Swiss Patent Document CH 619 764 discloses spring-loaded spreading elements between and alongside of the grate bars, the elements connecting all the grate bars and the side shields together being under the influence of spring forces. One problem in this connection consists of the cup springs, which must apply constant, uniform spring forces over a large temperature range and over a pressure range which varies due to thermal expansion of the grate bars and of the tie rod. These conditions are not assured in actual practice. The springs or movable rod parts are subjected to the high temperatures of the furnace and the residues of combustion material which are necessarily produced, thereby making it difficult to satisfy the necessary conditions.
European Patent Document EP B1 0 165 432 discloses a thrust grate in which the grate bars, which are arranged in the manner of roof tiles, have air inlet slots on their front surface for undergrate air, and in which the side shields are connected together by a tie rod. Cup springs are arranged between the grate bars for equalization of expansion. Profiled sealing sections arranged on the furnace wall have a well-defined play with respect to the side shields so that thermal expansion of the stationary grate bar supports is possible. EP B1 0 165 432 does not disclose how the movable rows of grate bars are constructure in this system nor how they cooperate with the side shields. The problem of the uncontrolled admission of undergrate air is, however, eliminated only in the case of relatively new furnaces. As soon as the surfaces of the grate bars have become worn due to the action of temperature and abrasion, they no longer lie against each other. The tie rod prevents the lowering of the row of grate bars onto the grate bars of the preceding row and gaps are thus produced between the upper and lower surfaces of the grate bars. Furthermore, in the event of repair, it is not possible to replace individual grate bars or to remove the approximately yard-long tie rod easily.